1. Field of the Invention
The present invention relates to a motor control circuit and a motor drive system using the same, and more specifically relates to a motor control circuit which detects that the rotating speed of the motor is stabilized and outputs a so-called ready signal such as a read write enabling signal suitable for such as a floppy disk drive (FDD), a hard disk drive (HDD) and an opto-magnetic disk drive apparatus, and further relates to a motor drive system using the same.
2. Description of Related Art
FIG. 3 is a conventional control circuit for a three-phase motor.
The motor control circuit comprises a motor 1, a sensing circuit 2, an input amplifying circuit 3, a motor drive circuit 4 (hereinbelow called a drive circuit 4) and a ready signal generating circuit 5.
The sensing circuit 2 is constituted by three Hall elements 2a as its major components and generates a detection signal dependent upon the rotation of the motor to thereby detect the rotating speed or the rotating phase of the motor 1.
The input amplifying circuit 3 is constituted by three differential which amplify 5a as its major components, amplifies the detected signal (see FIG. 4(a)) received from the Hall elements 2a in the sensing circuit 2 and output the same as a detection pulse P (see FIG. 4(b)) after waveshaping with a logic circuit for example.
The drive circuit 4 comprises a torque control circuit for example, which, determines the rotating condition of the motor 1 upon receipt of the detection pulse P and produces a drive voltage having a waveform as shown in FIG. 4(c), causing a drive current which operates to bring back the motor rotation number to a reference rotation number based upon the determined rotating condition in order to drive the motor 1 at a constant rotating speed.
In the motor control circuit, the motor 1, the sensing circuit 2, the input amplifying circuit 3 and the drive circuit 4 constitute a feedback loop such that under a steady state condition the rotation of the motor 1 is kept stable at a predetermined target rotating speed. In the motor drive system using this control circuit, the motor 1 is at a standstill during the circuit settling time immediately after turning on the power source or during exchange of the recording medium. At these instances, the drive circuit 4 stops the motor 1 upon receipt of a stop signal S from a host controller for example. Namely, the drive circuit 4 prevents rotation of the motor 1 upon receipt of the stop signal, and when the stop signal is released the motor 1 is accelerated to rotate from the standstill condition. Thereby a transient condition with regard to the motor rotation is caused before the motor reaches a steady state condition rotating at a predetermined reference rotating speed.
During this transient condition, the rotating speed of the motor is not yet stabilized; therefore if one of many operations of a drive apparatus such as an FDD or an HDD, for example an accessing operation such as read/write of data on the recording medium which is fitted over the .spindle of the motor 1 and is being rotated thereby, is performed, there arises a possibility of causing destruction of the recorded information on the recording medium or, further, causing destruction of the recording medium itself. For preventing such a possibility, the ready signal generating circuit 5 is provided in these kinds of motor control circuits.
The ready signal generating circuit 5 produces a ready signal K representing that the rotating speed of the motor 1 is stabilized, and outputs the same to an external device such as a host controller. When the host controller receives the ready signal K, the host controller treats the ready signal K as, for example, an enabling signal of read/write of data on the recording medium and initiates the read/write operation accordingly.
The ready signal generating circuit 5 delays by a predetermined time the release of the stop signal S, which has been applied from the host controller with a delay circuit 5a therein, and outputs the delayed timing signal as a ready signal K to thereby provide a predetermined waiting time for the operation of the host controller.
The predetermined delay time which produces the waiting time is determined by measuring the actual time required to stabilize the rotating condition of the motor in the drive device such (as an FDD or an HDD) after; starting the same and, further, by adding a margin in view of variability between drive devices. The determined waiting time is fairly longer than the measured time required until the motor rotation stabilizes.
In such a conventional ready signal generating method a ready signal is generated merely on expectation after waiting a predetermined time. Such method can not detect whether the motor actually reaches a stable rotating condition. In other words, even when the ready signal is received, it is not certain whether or not the motor rotation actually enters into a stable condition. Therefore, when the acceleration time of the motor is prolonged by some cause, no assurance is obtained that an accurate accessing operation can be performed. When an accessing operation to a recording medium is performed under an unstable condition, destruction of the recorded information or even destruction of the recording medium itself may be caused.
Further, in the conventional ready signal generating method, the delay time has had to be set fairly longer than the actual measured time. For this reason, it has taken time until an external device such as a controller would start an accessing operation for example, to several kinds of drive devices. As a result, response characteristics of the drive devices are reduced.